Nonlinear finite element modelling and parametric study of curved steel–concrete–steel double skin composite panels infilled with ultra-lightweight cement composite

The use of cold-formed steel (CFS) is becoming popular in residential and commercial building as a cost-effective alternative to traditional wood materials. CFS provides high strength-to-weight ratio, resulting in permitting lighter structure and longer spans. If proper design considerations are not made, this longer span and lighter structure can result in vibration serviceability issues that may affect building occupant comfort. The available design methods to calculate the dynamic properties of floor systems (i.e. Canadian Wood Council Method, CWC; Applied Design Council Design Method, ATC; and Eurocode, EC5) are used for the design of light-frame timber-based systems, CFS C-shape joists, and structural steel and concrete floor systems. The applicability of such methods to I-shape CFS joists is as yet unavailable. In addition, the North American Code for Cold-formed Steel structural Members (CSA-S136-07) provides specifications of ultimate and serviceability limit state design of C-shape joists rather than I-shape joists. As such, this research was divided into three parts. Part 1 presented the results of laboratory and field study on the vibration of a recently developed CFS I-shape joist called “iSPAN.” The main objective of the first part was to understand the dynamic characteristics of iSPAN floor system, recommend an adequate model for predicting the dynamic response and modal properties of floor systems, and correlate its results with engineered wood I-joists in order to aid the design process. Part 2 presented comparison between the experimental findings and available code provisions for the design of CFS joists at ultimate and serviceability limit states. The effect of web utility holes was also considered on the dynamic properties, and ultimate strength of iSPAN joists. Part 3 presented a finite-element modeling and its verification with the experimental findings of the tested samples. Also, part 3 extended the finite element modelling to analyse I- and C-shape CFS joists to determine their ultimate strength and serviceability, with and without the presence of utility holes in the webs. Since CSA-S137-07 does not provide design provisions for the edge-stiffened (i.e. lipped) holes, a practical-design-oriented parametric study, using the finite-element modelling, was conducted on CFS I- and C-shape members with circular, slotted and tri-slotted, edge-stiffened, holes under flexural loading. The optimized profile of the edge-stiffened holes was obtained using the elastic-buckling analysis. The post-buckling finite-element analysis was then utilized to determine member flexural strength as affected by utility hole geometry and web depth. Results showed that the edge-stiffened holes can significantly improve the flexural strength of CFS joists. The data generated from the parametric study was used to develop new design provisions to predict the flexural strength of such joists with the presence of edge-stiffened holes.

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The Effects of Crack Growth History on Fracture Toughness

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2019-93307 ◽

2019 ◽

Author(s):

M. A. Probert ◽

H. E. Coules ◽

C. E. Truman ◽

M. Hofmann

Keyword(s):

Fracture Toughness ◽

Finite Element ◽

Crack Growth ◽

Parametric Study ◽

Finite Element Modelling ◽

Crack Tip ◽

High Yield ◽

Element Modelling ◽

History Effects ◽

Apparent Fracture Toughness

Abstract The introduction of cracks into loaded versus unloaded components has a significant effect on the apparent fracture toughness within finite element modelling. The history effects of crack introduction can be beneficial to defect assessment procedures that do not consider prior plasticity specifically from crack introduction. It is assumed that as strain energy is released due to plastic deformation during crack formation a reduction in the energy available for crack propagation under fracture conditions is experienced. This can be characterized by the formation of a plastic wake behind the crack tip and leads to significant increases in load at critical J and other crack growth parameters for modelling situations. However experimental evidence validating this apparent fracture toughness increase are needed. A beneficial increase in apparent fracture toughness can prolong the life of components that might be taken out of service prematurely if history effects are not considered. This paper discusses a series of experimental and modelling approaches that have been taken to assess the magnitude of the benefit in increase of apparent fracture toughness by the manipulation of crack introduction history effects. An initial parametric study of material properties on the effect of introducing cracks into loaded and unloaded components indicates that most benefit be derived from high hardness, high yield materials such as Aluminum 7000 series alloys. Further work has been carried out with experimental C(T) specimens of Aluminum Alloy 7475 T7351. Cracks were introduced by fatigue into the samples. One set of specimens was fatigued with a low mean load and the other with a high mean load, this was achieved by keeping a consistent ΔKI between specimens and changing the load ratio one set of specimens. Fracture test results indicate that the influence of prior plasticity on fracture initiation is much subtler in experimental trials than in the finite element model. Crack growth resistance curves and neutron diffraction results measuring the residual stress created ahead of the crack tip by this method are be discussed and contrasted with the parametric study and finite element modelling of the two different crack introduction scenarios.

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